Report on heavy metal pollution in farmland
Last update time : 04/01/2019
Environmental pollution survey —Heavy harmful metal detection
Induced electromagnetic detection
Electrical Resistivity Tomography environmental application
The geophysical survey area are a large scale harmful metal soil polluted site.which is about 5000 square meters.
The field testing is mainly as the ERT resistivity method and induction electromagnetism method. Which also combined with the existing drilling and excavation XRF sieve test data, verify the mode field of soil pollution characteristics and depth of local electric change trend, and the specific geophysical images depicting underground pollution and formation condition, and accurate assessment of soil pollution depth and high concentration the soil heavy metal pollution in the region, providing reliable information for future construction.
The silver market area has a detection range of about 5,000 square meters. It plans to conduct a comprehensive grid-based induction electromagnetic survey together with a gridded high-density resistivity method to assess the applicability of geophysical techniques to sites contaminated with heavy metals. The site is contaminated by heavy metal soils. According to the background information, the average pollution depth is estimated to be 0.5-2 meters. Detection of the distribution range of buried objects is the fastest with induction electromagnetism method. It is suitable for rapid general survey and has the advantages of quick and accurate survey , Especially for contaminated soils that are highly conductive and vary greatly in their electrical properties from their original counterparts. The vertical actual depth and buried property determination are determined by high-density resistivity method or drilling sampling analysis. The configuration and quantity of detection are shown in Figure 2-1 and Table 2-1. The working photos of the site are shown in Figure 2-2.
Induction Electromagnetic Method Results
According to the results of the detection, the red scale in the graph shows the high conductivity (low resistivity), while the blue-purple color belongs to the low conductivity range (high resistivity). In the integrated conductivity graph (a) The overall conductivity is high, the assessment of the high conductivity of more than 1 value of the formation, covering the entire survey area, assessment of 0 to 2 meters of heavy metals are within the soil pollution distribution, which in the site west of the obvious high conductivity stratigraphic distribution, showing more than 30 mS / m of the red level, presumed to be deeper areas of heavy metal contaminated soil; in (b) the comprehensive susceptibility map, the magnetic susceptibility represents the degree of magnetization of the object after the magnetic field is applied, especially in the soil contains very high magnetic source objects , Such as iron, nickel, copper, zinc, cadmium, etc. The results show that the overall magnetic susceptibility is high, belong to the high magnetic susceptibility strata, greater than the value of 0.4 red stratum, presumed to be serious heavy metal soil pollution distribution area.
Integrated multi-frequency induction electromagnetic detector results show that, as the site belongs to a large number of heavy metal distribution of soil, and high concentrations of heavy metal soils have a strong magnetic susceptibility characteristics, EM survey has a rapid investigation of electrical properties were significantly different soil pollution distribution of heavy metals ability. According to the characteristics of different contaminated soils and landfills, the planned grid density can be planned. The daily survey efficiency is about 10,000 ~ 20,000 square meters, which helps to identify areas with high concentrations of contaminated soil and provide reference information for subsequent soil remediation.
High-density resistance method results
According to the results of 12 ERT resistivity tests, the resistivity of normal soil is obviously different from that of contaminated soil. The average depth of heavy metal contaminated soil is about 1.2-1.8 m, and the depth of heavy metal contaminated soil can be plotted in the result map. Analysis of contaminated soil resistivity range of about 10 ~ 80 Ohm-m, but does not recommend the use of resistivity to identify high concentrations of heavy metal contaminated soil, still a sufficient number of sample analysis to prove. For example, the S-02 sampling point (very severe) on the CX-2 survey line, but not the lowest resistivity, shows greater sand permeability as heavy metals tend to seep into the deep with rainwater, causing grit and heavy metal contaminated soils Showing a comprehensive effect of pollution, thereby affecting the resistivity slightly higher.
3D results and cutaway
The results of resistivity of CX1 ~ CX12 line with high-density resistivity method can be used to build a 3D model of 3D high-density resistivity. The 3D results are shown in Fig. 4-15. The 3D isosurface results are shown in Fig. 4 -16 ~ Figure 4-17 shows that the overall shallow are low resistivity stratigraphy, at the same time analysis of 50 Ohm-m-80 Ohm-m below the 3D low resistivity distribution region, the low resistivity distribution results and the induction of electromagnetic The results are basically in line with the scope of large-scale and deep heavy metal contaminated soil are mainly distributed in the west of the site, the 3D results show downward resistance characteristics of the average depth of about 1.2 to 1.8 meters, and even the local low resistance depth of 2.2 ~ 2.5 meters. The depth of heavy metal pollution in the soil on the west side of the assessment site is deep. The XRF sampling point S02 is located here (65 meters on the CX2 survey line) and the XRF measurement value at a depth of 1 meter is still very high. Comparisons of deeper soil samples collected on the west side of the site.